1. Field of the Invention
The present invention relates to a light emitting compound for an organic electroluminescent device and an organic electroluminescent device using the same, and more particularly, to a light emitting compound used in an organic electroluminescent device that is a self-emission type display device and has a wide viewing angle, an effective contrast and a fast response time, and an organic electroluminescent device using the emitting compound.
2. Description of the Related Art
An organic electroluminescent (hereinafter referred to as “EL”) device has advantages in that the viewing angle is wide, the contrast is significant, and the response time is as fast as a self-emission type display device.
An EL device is divided into an inorganic EL device and an organic EL device depending on materials to form an emitting layer, wherein the organic EL device has advantages in that the luminance, the driving voltage and the response speed characteristics are improved compared to the such characteristics of the inorganic EL device, and the organic EL device is displayed in multi-colors.
An ordinary organic EL device has a structure in which the anode is formed on an upper part of the substrate, and the hole transport layer, the emitting layer, the electron transport layer and the cathode are sequentially formed on an upper part of the anode, wherein the hole transport layer, the emitting layer and the electron transport layer are organic thin films formed from organic compounds.
The driving principle of an organic EL device having the foregoing structure is as follows.
If a voltage is applied between the anode and the cathode, the holes injected from the anode are transferred to the emitting layer via the hole transport layer. On the other hand, electrons are injected into the emitting layer from the cathode via the electron transport layer, and carriers are recombined in the emitting layer region to produce an exciton. The exciton is changed from the excited state to the ground state, emitting fluorescence from the emitting layer accordingly so that an image is formed.
On the other hand, although compounds such as diphenylanthracene, tetraphenylbutadiene and a distyrylbenzene derivative have recently been developed as a blue emitting material, and the IDEMITSU CORPORATION has recently developed a styryl compound (PCT/JP2001/7295) and an arylamine compound (PCT/JP2001/7477) as a blue emitting material, the blue emitting materials have disadvantages in that the color purity is low, and the life time is decreased due to a lower thin film stability.
Although, as disclosed in U.S. Pat. No. 5,141,671, the EASTMAN KODAK CORPORATION developed Balq, which is an aluminum complex, as a blue emitting material in 1992, Balq is now used as a hole blocking layer rather than a blue emitting material due to its ineffective emission efficiency and color coordinates (0.18, 0.27). Therefore, there is a need to develop a blue emitting material having high heat resistance, emission efficiency and color purity.